Polyine mit <i>tert</i>‐Butyl‐Endgruppen: kristallographischer Nachweis einer reduzierten Bindungslängenalternanz

Chalifoux, Wesley A.; McDonald, Robert; Ferguson, Michael J.; Tykwinski, Rik R.

doi:10.1002/ange.200902760

Cited by 27 publications

(15 citation statements)

References 60 publications

Supporting

Mentioning

Contrasting

Unclassified

Order By: Relevance

“…A key question to be answered based on structural analysis of cumulene bond lengths is: Do cumulenes show experimental evidence of reduced BLA as a function of increasing length? While this question has been answered for polyynes, [29] to date there has been insufficient crystallographic data to offer an answer for cumulenes. Computational chemists have frequently studied BLA in cumulenes.…”

Section: Methodsmentioning

confidence: 99%

Synthesis and Structure of Tetraarylcumulenes: Characterization of Bond‐Length Alternation versus Molecule Length

et al. 2013

View full text Add to dashboard Cite

Dedicated to Professor FranÅois Diederich on the occasion of his 60 th birthday Chains composed of sp-hybridized carbon atoms have been explored for decades because of their unique linear structure and interesting physical properties. [1] More recently, the wirelike nature of sp-carbon oligomers has inspired a variety of studies that aim to evaluate these structures as components in nanometer-sized devices. [2] Particularly interesting is the reported formation of such wires linking graphene nanoribbons, offering the prospect of all-carbon-based devices. [2d-f, 3] Molecules composed of a skeleton of sp-hybridized carbon atoms can be constructed from a framework of either polyynes (alternating single and triple bonds) or cumulenes (cumulated double bonds). The chemistry of polyynes has been advanced to systems as long as 44 consecutive carbon atoms (22 acetylene units), [4] and studies have shed considerable light on the physical and optoelectronic properties of polyynes. [5] However, the study of cumulenes has lain essentially dormant since early work [6,7] reported by Kuhn [8,9] and Bohlmann. [10,11] Thus, there remain many unanswered questions about the physical properties of this intriguing class of linear molecules. To date, UV/Vis spectroscopy has been the most useful method for the characterization of cumulenes, [12] and analyses of cumulenes show a lowering of the lowest-energy electronic absorption (l max ) as a function of length, such as that for [n]Ph and [n]Cy (n = 3, 5, 7, 9, Figure 1). [9][10][11] Obviously, changes in l max versus molecular length are intricately dependent on structure and on the degree of bond-length alternation (BLA, defined as the bondlength difference between the two central-most double bonds of the cumulene chain). Recent theoretical studies predict that the BLA for cumulenes will rapidly approach zero (BLA 0.01), [13][14][15] that is, Peierls distortion is essentially absent. [16] Experimentally, X-ray crystallographic analysis would provide an opportunity to confirm or refute theoretical trends in BLA as a function of cumulene length. Unfortunately, few solid-state structures have been reported for cumulenes, and data for [n]cumulenes with n > 5 are not available. The results presented herein offer an answer to the important question of BLA in long cumulenes.It was clear from the onset of the study that the synthesis and solid-state analysis of long [n]cumulenes (n > 5) would be challenging, because available reports emphasized that these species were not typically stable enough for isolation. [6] In order to stabilize the cumulene core through steric shielding, initial efforts targeted formation of the [n]tBuPh series of cumulenes ( Figure 1). It quickly became clear, however, that the di(tert-butyl)phenyl (R = tBu 2 C 6 H 3 ) groups do not afford a sufficient stabilizing force to easily isolate the [7]-and [9]tBuPh cumulenes, and our attention then switched to the [n]Mes series.Synthesis of [3]tBuPh began with the formation of 1 a through reaction of the Li-acetylide of...

show abstract

Section: Methodsmentioning

confidence: 99%

Synthesis and Structure of Tetraarylcumulenes: Characterization of Bond‐Length Alternation versus Molecule Length

et al. 2013

View full text Add to dashboard Cite

show abstract

“…Durch schützende Endgruppen konnten Oligoethinylene mit bis zu 14 konjugierten Dreifachbindungen synthetisiert und isoliert werden. Beispiele hierfür sind Me‐(CC) 6 ‐Me,210 Pfp‐(CC) 8 ‐Pfp,211 (Pfp=Pentafluorphenyl), (CH 3 ) 3 C‐(CC) 10 ‐C(CH 3 ) 3 212, 213 und TIPS‐(CC) 10 ‐TIPS 214. Für letzteres Beispiel wurde eine Reihe von Bis(triisopropyl)‐substituierten Derivaten TIPS‐(CC) n ‐TIPS mit dynamischer Differenzkalorimetrie (DSC) untersucht.…”

Section: Carbonisierung Energiereicher Vorstufenmoleküleunclassified

Halogenated Benzene Cation Radicals

Molski

Mollenhauer

Gohr

et al. 2012

Chemistry A European J

View full text Add to dashboard Cite

The halogenated benzenes C(6)HF(5), 2,4,6-C(6)H(3)F(3), 2,3,5,6-C(6)H(2)F(4), C(6)F(6), C(6)Cl(6), C(6)Br(6), and C(6)I(6) were converted into their corresponding cation radicals by using various strong oxidants. The cation-radical salts were isolated and characterized by electron paramagnetic resonance (EPR) spectroscopy and by single-crystal X-ray diffraction. The thermal stability of the cation radicals increased with decreasing hydrogen content. As expected, the cation radicals [C(6)HF(5)](+) and 2,3,5,6-[C(6)H(2)F(4)](+) had structures with the same geometry as C(6)HF(5) and 2,3,5,6-[C(6)H(2)F(4)]. In contrast, the cation radicals [C(6)F(6)](+), [C(6)Cl(6)](+), and possibly also [C(6)Br(6)](+) exhibited Jahn-Teller-distorted geometries in the crystalline state. In the case of C(6)F(6)(+)Sb(2)F(11)(-), two low-symmetry geometries were observed in the same crystal. Interestingly, the structures of the cation radicals 2,4,6-[C(6)H(3)F(3)](+) and C(6)I(6)(+) did not exhibit Jahn-Teller distortions. DFT calculations showed that the explanation for the lack of distortion of these cations from the D(3h) or D(6h) symmetry of the neutral benzene precursor was different for 2,4,6-[C(6)H(3)F(3)](+) than for [C(6)I(6)](+).

show abstract

“…[16] Notably, the FBW rearrangement has recently evolved into a valuable synthetic methodology for the preparation of polyyne structures, which can be accessed by treatment of 1,1-dibromo-2,2-dialkynyl-A C H T U N G T R E N N U N G ethenes with n-butyllithium (nBuLi). [17] Developing a similar protocol for the synthesis of diaminoalkynes required the preparation of the corresponding 2,2-dibromo-1,1-ethenedi-A C H T U N G T R E N N U N G amines of type 2 (Scheme 2), which, to the best of our knowledge, have not been described in the literature to date, although a limited number of dichloro derivatives have been reported that were obtained unexpectedly [18] or as byproducts. [19] a,a-Dibromoolefins are generally prepared from aldehydes or ketones by a dibromoolefination protocol by using Ph 3 P/CBr 4 ; [20] however, the low reactivity of the corresponding N,N,N',N'-tetrasubstituted ureas precludes the application of this method for the preparation of compounds 2.…”

mentioning

confidence: 97%

A Novel Synthetic Approach to Diaminoacetylenes: Structural Characterization and Reactivity of Aromatic and Aliphatic Ynediamines

Petrov

Daniliuc

Jones

et al. 2010

Chemistry A European J

View full text Add to dashboard Cite

Polyine mit tert‐Butyl‐Endgruppen: kristallographischer Nachweis einer reduzierten Bindungslängenalternanz

Cited by 27 publications

References 60 publications

Synthesis and Structure of Tetraarylcumulenes: Characterization of Bond‐Length Alternation versus Molecule Length

Synthesis and Structure of Tetraarylcumulenes: Characterization of Bond‐Length Alternation versus Molecule Length

Halogenated Benzene Cation Radicals

A Novel Synthetic Approach to Diaminoacetylenes: Structural Characterization and Reactivity of Aromatic and Aliphatic Ynediamines

Contact Info

Product

Resources

About